In one technology, for example, there is a technique as disclosed in JP 2010-164356 A for detecting an obstacle existing ahead in a travel direction of the vehicle. In this technique, reflected waves of spherical surface transmission waves that have been emitted by an in-vehicle sonar are captured, so that the obstacle is detected. Here, in order to distinguish between the reflected wave from a road surface and the reflected wave from an obstacle, a threshold pattern for removing the reflected wave from the road surface is set and the threshold pattern is removed from the reflected wave that has been captured, so that the obstacle is detected.
In the technique as disclosed in JP 2010-164356 A, however, a road surface and an obstacle can be distinguished from each other, but the type of the obstacle cannot be determined. Therefore, when acceleration suppression control is performed as a drive assist for suppressing a contact between a vehicle and an obstacle such as a wall or another vehicle, the acceleration suppression control is activated for the obstacles, such as a curb stone, edge stone, or grass (natural thing), for which the acceleration suppression is not needed, making a troublesome situation.